This invention relates to pressure relief systems and more specifically to a pressure relief system for use on a hydrocarbon tank truck to minimize hydrocarbon pollution of the atmosphere caused by the pressure inside the tank.
Current government regulations require in some localities that underground hydrocarbon storage tanks for service stations have facilities for preventing the flow of hydrocarbon vapors into the atmosphere when these tanks are filled. One such system includes the use of a pipeline to carry the vapor from the underground tank back to the tank truck. One of the problems encountered in using this system is the variance in temperatures of the gasoline in the tank truck and the temperature of the gasoline and the vapor in the underground storage tank. These temperature variances can build up excess pressure inside the tank truck or inside the underground storage tank during filling. Additional vapors are generated by the turbulence created during filling. When the hose connections to the tanks are broken after the underground storage tank is filled, the vapor pressure inside these tanks can often cause hydrocarbon vapors to be forced into the atmosphere.